MR imaging of edema accompanying benign and malignant bone tumors

Detection of areas with viable remnant tumor in postchemotherapy patients with Ewing's sarcoma by dynamic contrast-enhanced MRI using pharmacokinetic modeling

An approach is presented for monitoring the effects of neoadjuvant chemotherapy in patients with Ewing's sarcoma using dynamic contrast-enhanced perfusion magnetic resonance (MR) images. For that purpose, we modify the three-compartment pharmacokinetic permeability model introduced by Tofts et al. (Magn Reson Med 1991;17:357-67) to a two-compartment model. Perfusion MR images acquired using an intravenous injection with Gadolinium (Gd-DTPA) are analyzed with this two-compartment pharmacokinetic model as well as the with an extended pharmacokinetic model that includes the (local) arrival time t(0) of the tracer as an endogenous (estimated) parameter. For each MR section, a wash-in parameter associated with each voxel is estimated twice by fitting each of the two pharmacokinetic models to the dynamic MR signal. A comparison of the two wash-in parametric images (global versus local arrival time) with matched histologic macroslices demonstrates a good correspondence between areas with viable remnant tumor and a high wash-in rate. This can be explained by the high number and permeability of the (leaking) capillaries in viable tumor tissue. The novel pharmacokinetic model based on a local arrival time of tracer results in the best fit of the wash-in rate, the most important factor discerning viable from nonviable tumor components. However, parameter estimates obtained with this model are also more sensitive to noise in the MR signal. The novel pharmacokinetic model resulted in a sensitivity between 0.22 and 0.60 and a specificity between 0.61 and 1. The model based on a global arrival time gave sensitivities between 0.33 and 0.77 and specificities between 0.58 and 0.99. Both statistics are computed as the fraction of correctly labeled voxels (viable or nonviable tumor) within a specified ROI, which delineates the tumor. We conclude that the added value of estimating the local arrival time of tracer first manifests itself for moderate noise levels in the MR signal. The novel pharmacokinetic model should moreover be preferred when pharmacokinetic modeling is applied on the average signal intensity within a ROI, where noise has less effect on the fitted parameters.

Transient bone marrow oedema: a variant pattern of sacral insufficiency fractures

A 71-year-old woman presenting with severe low back pain was found to have a large oval area of increased sacral uptake on Tc-99m MDP scan, with corresponding T1-hypointense and T2-hyperintense areas on magnetic resonance (MR) images, highly suggestive of malignancy. Open biopsies showed only callus formation. The patient responded clinically to conservative measures, with twice-repeated follow-up Tc-99m MDP and MR scans documenting resolution of transient bone marrow oedema. We suggest that this form of marrow oedema represents a variant pattern of sacral insufficiency fractures.

99mTc-nanocolloid scintigraphy for assessing osteomyelitis in diabetic neuropathic feet

Distinguishing osteomyelitis from neuropathic osteoarthropathy in diabetic feet is a common and difficult clinical problem with no highly accurate discriminatory investigation. This study assesses the novel use of marrow scintigraphy and compares it with magnetic resonance imaging (MRI) for the diagnosis of osteomyelitis in neuropathic osteoarthropathic diabetic feet. Nine diabetic patients with chronic foot ulcers were prospectively assessed independently using 99mTc-nanocolloid scintigraphy and MRI. Those patients showing features of osteomyelitis underwent percutaneous bone biopsy or surgical ray excision for histological confirmation. Other patients were followed up clinically for a minimum of 6 months to exclude osteomyelitis. Marrow scintigraphy, in agreement with MRI, demonstrated all four cases of biopsy proven osteomyelitis and excluded three cases with neuropathic osteoarthropathy alone. One case of suspected osteomyelitis of the ankle on marrow scintigraphy, but not MRI, was not confirmed clinically. One case of suspected osteomyelitis on both imaging modalities was shown on biopsy to demonstrate changes of avascular necrosis but not osteomyelitis. In this study 99mTc-nanocolloid scintigraphy shows a sensitivity of 100% and specificity of 60%. An important false positive result is seen with avascular necrosis, both on marrow scintigraphy and on MRI. Although larger studies are needed to evaluate this technique, 99mTc-nanocolloid marrow scintigraphy may be an alternative to MRI for assessing diabetic feet for osteomyelitis.

Magnetic resonance imaging of the musculoskeletal system. Part 9. Primary Tumors

Magnetic resonance imaging, because of its exquisite soft tissue contrast, has dramatically improved the ability to preoperatively stage primary osseous and soft tissue neoplasms. This technique also has allowed the monitoring of the effects of chemotherapy and the screening for recurrence of neoplasms. The role of magnetic resonance imaging in the preoperative evaluation of the patient with a suspected primary osseous or soft tissue neoplasm is outlined, instances where magnetic resonance imaging potentially may make a specific diagnosis are outlined, the importance of gadolinium enhancement as an adjunct to native magnetic resonance imaging is stressed, and an algorithm for followup of patients after chemotherapy or definitive surgical treatment is presented. In all cases, the magnetic resonance images should be correlated with the plain film, which is still an important aspect of the diagnosis of osseous lesions.

Osteoid osteoma and osteoblastoma of the spine. Factors associated with the presence of scoliosis

STUDY DESIGN

A retrospective study of 44 museum cases of spinal osteoid osteoma or osteoblastoma and a meta-analysis using 421 additional cases from a review of the literature.

OBJECTIVES

To identify the factors that are associated with the development of scoliosis in these patients.

SUMMARY OF BACKGROUND DATA

Painful scoliosis is a well recognized presentation of spinal osteoid osteoma and osteoblastoma and is considered to be secondary to pain-provoked muscle spasm on the side of the lesion. Previous studies have been based on small numbers of patients that did not permit statistical validation of the reported observations.

METHODS

Eight factors were assessed including: age, gender, duration of symptoms, site of lesion in the spine, vertebral level of lesion, site of lesion in the individual vertebra, type of lesion, and Cobb angle at presentation. Reports were reviewed only if the presence or absence of scoliosis could be determined. Statistical analyses initially were performed on the museum cases and then on a combination of museum cases and cases from the literature.

RESULTS

Overall, 63% of subjects had scoliosis. The lesions were typically present on the concave aspect of the curve. Three cases of scoliosis from the literature involved lesions that were reported to be on the convexity. Scoliosis is significantly more common in cases of osteoid osteoma than in cases of osteoblastoma (P < 0.0001); lesions are more common in the thoracic and lumbar regions than in the cervical region (P < 0.0001), in lower cervical region than in the upper cervical region (P value = 0.0027), and they are more commonly located to one side of the midline (P < 0.0001). Age, gender, and duration of symptoms were of no significance.

CONCLUSIONS

The findings support the concept that scoliosis is secondary to asymmetric muscle spasm in patients with spinal osteoid osteoma or osteoblastoma.

Overuse edema in the bone marrow of the hand: demonstration with MRI

In MRI of the skeleton, marrow edema is a frequent finding that can be caused by avascular necrosis, fracture, bone bruises, transient osteoporosis, osteomyelitis, primary tumors, metastases, and altered biomechanical properties. We examined a 29-year-old woman golfer with mild pain and swelling of the proximal phalanx II of the left hand. No signs of a stress fracture were seen on the MR images or plain radiographs. MRI revealed increased signal intensity on T2-weighted images in the metacarpal and proximal phalanx II in the left hand. We concluded that bone marrow edema may be the result of physiologic bone response to stress and may not necessarily correspond with severe trauma. Our case complements recent observations outlining the influence of altered biomechanics as a reason for marrow edema.

Does magnetic resonance imaging make a difference for patients with musculoskeletal sarcoma?

MR imaging has had an unparalleled impact on the treatment of patients with musculoskeletal sarcoma. Basically, the high accuracy of local staging has made the introduction of reconstructive and limb salvage procedures instead of amputation of disarticulation available to the majority of patients with musculoskeletal sarcoma. Pre-operative work-up with MRI is not only more accurate, but also much faster and cheaper than the conventional work-up. Staging is the single most important reason for performing MR imaging in patients with musculoskeletal tumours. The impact of MR specificity is less dramatic but the benefit to the patient is an increased safety margin. When diagnostic errors with devastating consequences are made nowadays, it is usually because the proper protocol has not been followed. A patient with a potentially malignant, or equivocal, musculoskeletal mass deserves to have a combined radiographic-MRI examination prior to invasive procedures. MRI does not currently have a major impact on chemotherapy decisions and colour Doppler ultrasound has a higher accuracy than MRI. However, selected cases, i.e. intraosseous tumours, dynamic Gd-enhanced MRI, can replace colour Doppler ultrasound.

MRI characteristics of chondroblastoma

We report a retrospective study of MR imaging of 16 patients with histologically proven chondroblastoma, 12 at primary presentation and four clinically suspected recurrences. In all the primary cases MR imaging showed a lobulated low signal intensity (SI) rim. Low SI foci within the tumour were present in 11 out of the 12 cases and corresponded to calcification seen on radiographs or CT. Bone marrow oedema was also present in 11 out of 12 cases and an adjacent joint effusion in eight out of 12. The STIR sequence was of particular value, giving optimal delineation of marrow and soft tissue oedema. Of the suspected recurrences one showed peritumoral oedema and was subsequently proven histologically. Three showed no peritumoral oedema and subsequent histology was negative in these cases. The presence or absence of oedema may be a useful indicator of tumour activity although further study is required.

Can MRI predict the histopathological response in patients with osteosarcoma after the first cycle of chemotherapy?

The magnetic resonance (MR) changes after one cycle of chemotherapy were compared with the prechemotherapy studies in 39 patients with osteosarcoma, in order to identify MR changes which can be used to assess early response to chemotherapy. Measurements of total tumour volume, signal intensity, and tumour enhancement of the intra- and extraosseous tumour component were performed. Change in the amount of oedema was subjectively assessed. Changes observed were correlated with histopathological response. Changes in tumour volume and of the signal intensity of the extraosseous tumour component on T2-weighting were the only two parameters which correlated significantly (P < 0.05) with histopathological response. Increase of tumour volume is the most significant parameter and indicates poor response (sensitivity 89%, specificity 73%). Only one good responder showed increase of tumour volume. Decreased or stable tumour volume was observed in both good and poor responders. Increase of signal intensity was found exclusively in five poor responders (sensitivity 100%, specificity 23%). Decreased or stable signal intensity was observed in both good and poor responders. Changes in the amount of oedema and contrast enhancement could not predict response at an early stage. We conclude that increase of tumour volume and increase of T2 signal intensity of extraosseous tumour can be predictive for poor response. MR criteria are not helpful in the early identification of good responders.